In the completion of oil wells it is customary to have a succession of smaller diameter boreholes as a function of depth, each of the boreholes being lined with a tubular pipe member, and each of which are successively cemented in place. The column of cement between the outer surface of the string of pipe and the borehole wall supports the pipe and prevents fluid migration.
As a matter of terminology, a string of pipe extending from the surface is commonly called a casing. The surface borehole is drilled a few thousand feet and the surface casing inserted in the borehole and cemented in a conventional manner. Thereafter, a smaller diameter bit is used to drill another section of open borehole and a string of casing can be inserted into the second borehole which extends to the surface and is cemented in place in a conventional manner. Alternatively, a liner can be suspended in the lower end of the surface casing and cemented in place. A liner is a string of pipe which is hung at the lower end of another string of pipe which is already in the wellbore. After the next casing or liner is in position in the borehole, the drilling is continued to another depth and a liner string of pipe is suspended in the lower end of the next above string of pipe and cemented in place. The drilling operations continues thusly until the desired depth is reached.
To position and cement a liner in a string of casing, the liner is made up with the usual bottom hole equipment which includes a casing shoe, a float collar and plug catchers and is connected up to the desired length. At the top of the liner is a liner hanger, which is an assembly having slip elements which are normally retracted while going into the borehole and which are released downhole when the setting of the liner hanger is desired. The liner hanger is lowered into the borehole by a setting tool which attaches to the liner hanger and a string of pipe attached to the setting tool. At the desired location where the casing shoe is preferably located above the bottom of the open borehole, the liner hanger is set in the next above casing by actuating the setting tool to set the slips on the liner hanger. Upon setting the liner hanger, the weight of the liner is suspended by the liner hanger on the next above casing. The liner is then cemented by pumping cement through the string of pipe, through the liner and into the annulus between the liner and the open borehole. This setting tool and running string are then removed. After the cement is set up, remaining cement in the liner is removed by drilling through the liner and the destructible cementing equipment in the lower end of the liner.
Liner hangers can be set either mechanically of hydraulically. Mechanically set liner hangers are set by manipulation of the setting tool and often present problems in operation of the setting and release of the setting tool from the liner hanger particularly in deep or deviated wells. Hydraulic operated setting tools operate by providing a pressure barrier in the string of pipe below the liner hanger and pressuring up the string of pipe above the liner hanger to produce a relative movement between a slip and expander to set the slips on the liner hanger into gripping engagement with the well casing. Hydraulic hangers also fail to set from time to time and when either a mechanical or hydraulic tool fails to operate it is necessary to remove the entire string of pipe and utilize another tool or liner hanger which involves considerable expense.
The liner hanger itself is designed to have a minimum clearance between the outer surfaces of the liner hanger and the liner or casing through which it passes and provides the largest possible bore through the center of the liner hanger. Since there is always drilling mud in the well bore, for control purposes, insertion of the tool in the well bore can be a problem because of the hydraulic effect of fluid in the casing.
Examples of prior art liner hangers are found in the following U.S. patent:
______________________________________ U.S. Pat. No. Issued Inventor ______________________________________ 3,993,128 11/23/76 Braddick 3,999,605 12/28/76 Braddick 3,934,652 1/27/76 Cochran 4,287,949 9/08/81 Lindsey ______________________________________
It is a purpose of the present invention to provide a liner hanger and setting tool which can be set and reset hydraulically as well as set mechanically so that the tool can be repositioned in a borehole without requiring a round trip and to make the setting mechanism retrievable with the setting tool so that it may be reusable.